The present invention relates to an airbag apparatus that inflates an airbag when an impact is applied to a vehicle due to collision, thereby protecting an occupant against the impact.
An airbag apparatus is effective as an apparatus for protecting the occupant against an impact applied to a vehicle due to collision. Such an airbag apparatus includes an airbag in the form of a bag and an inflator for supplying inflation gas into the airbag.
One mode for such a type of airbag apparatus is a side airbag apparatus for protecting an occupant against, for example, impact from a side collision. In this side airbag apparatus, the foregoing airbag in a folded state and the inflator are incorporated into a seat back of a vehicle seat. In the side airbag apparatus, when an impact is applied to a member constituting a side part of the vehicle (body side portion), for example, a side door, from a side, the inflation gas is supplied from the inflator into the airbag. The airbag is inflated and deployed by the inflation gas and then, bursts out of the vehicle seat, with a part being left in the seat back. The airbag is inflated and deployed forward in a small space between the occupant seated in the vehicle seat and the body side portion. The inflated and deployed airbag is interposed between the occupant and the body side portion entering into the vehicle, thereby restraining the occupant as well as absorbing energy of the impact to protect the occupant against the impact.
Another mode for a side airbag apparatus is an airbag, the inside of which is not partitioned (hereinafter referred to as “Prior Art 1”).
Japanese Laid-Open Patent Publication No. 10-67297 proposes still another mode for a side airbag apparatus in which a partition portion for partitioning an airbag into an upper airbag and a lower airbag is provided using a pressure regulating valve (pressure control valve) so that the lower airbag is inflated earlier than the upper airbag by the action of the pressure regulating valve (hereinafter referred to as “Prior Art 2”). A word inside a parenthesis following the name of each member represents the name of the member used in the publication. In the side airbag apparatus according to Prior Art 2, the airbag first inflates up to the height of the hip of the occupant and then, inflates up to the height of the chest. Thus, the impact can be absorbed more efficiently.
In the side airbag apparatus, the body side portion enters toward the inside of the vehicle due to the side impact, thereby pressing the airbag onto the occupant. With this pressure, the occupant is subjected to a load of the impact through the airbag. The load is expressed by a product of an area where the occupant is pressed by the airbag, that is, a pressure-receiving area of the occupant on the side of the airbag and an internal pressure of the airbag. To protect the occupant against the impact, it is desired that the load reach a predetermined value within a short time from start of entry of the body side portion and then, maintains the predetermined value irrespective of an entry amount (stroke) of the body side portion.
However, according to Prior Art 1, since the internal pressure and the pressure-receiving area increase with an increase in the entry amount of the body side portion, the load received by the occupant from the airbag gradually increases as the body side portion enters. The load does not reach the predetermined value until the body side portion enters to some extent. In addition, the load continues to increase even after it reaches the predetermined value and finally, exceeds the predetermined value. As a result, sufficient protection of the occupant against the impact cannot be started before the load has reached the predetermined value. After the load reaches the predetermined value, the occupant receives a load that is larger than the predetermined value through the airbag.
Prior Art 2 does not disclose specific configuration of the pressure regulating valve. For this reason, the relationship between the load received by the occupant from the airbag and the entry amount of the body side portion is unclear.
The load characteristics can be improved by providing the pressure regulating valve with a more complicated configuration. However, it causes an increase in costs of the airbag apparatus.
Such problem occurs in the above-discussed side airbag apparatus as well as other types of airbag apparatuses.